[llvm] [AArch64] Signed comparison using CMN is safe when the subtraction is nsw (PR #141993)

[David Green via llvm-commits]

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@@ -602,3 +602,49 @@ define i1 @almost_immediate_neg_ugt_64(i64 %x) {
   %cmp = icmp ugt i64 %x, -16773121
   ret i1 %cmp
 }
+
+define i1 @cmn_nsw(i32 %a, i32 %b) {
+; CHECK-LABEL: cmn_nsw:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    cmn w0, w1
+; CHECK-NEXT:    cset w0, gt
+; CHECK-NEXT:    ret
+%sub = sub nsw i32 0, %b
+%cmp = icmp sgt i32 %a, %sub
+ret i1 %cmp
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davemgreen wrote:

Indent the code in the function a little

https://github.com/llvm/llvm-project/pull/141993